This invention relates generally to resilient sealing liners for closure caps, and more particularly to a cap construction and a method for inserting such liners therein without causing damage to either the cap or the liner.
A number of arrangements for retaining liners in closures have been proposed and produced. The most common approach has been to employ a series of circumferentially spaced, inwardly protruding lugs adjacent the top wall of a closure cap, and to press the liner into position such that it by-passes the lugs. In so doing, in almost every case there occurred a significant deformation of the liner, since the diameter of the latter had to be somewhat larger than the distance between opposite lugs. The deformation occurred as a result of both bending of the liner along a diameter, and compression of the edge portion thereof, as it was forced by the lugs. Although this method of retaining such liners has found wide acceptance in the industry, there existed a tendency for the liners to separate during subsequent handling of the cap. An example of such a construction is illustrated in U.S. Pat. No. 4,381,840; the problem associated with the liners falling out is addressed in column 3 of the patent, lines 34-41.
Other examples of retainer lugs are shown in U.S. Pat. Nos. 3,612,325; 2,904,837; 1,937,492. U.S. Pat. No. 2,039,757 describes an arcuate bead that extends for a major part of the circumference of the cap. The patent mentions an angle of 250.degree. as having been found to provide good results.
Other methods for securing a liner have involved gluing the part in position in the cap. This had the obvious disadvantage that the integrity of the bond was uncertain. Moreover, it was always difficult to determine exactly how much glue or adhesive would be required in order to provide adequate adhesion, yet avoid the tendency for the glue to ooze out past the liner. Glue is thus considered not a good solution to the problem.
A still further alternative was to rely upon the threads of the cap in order to retain the liner. Under such circumstances, the diameter of the liner was made sufficiently large that it would not easily by-pass such threads. In order to insert the part, it was forcibly pressed past the threads, and usually occupied a recessed area lying between the upper end of the threads and the cap top wall. This arrangement usually resulted in worse damage to the liner, since the threads of the cap, being constituted of relatively stiff plastic, did not yield to any significant extent; instead they caused compression of the edge or periphery of the liner. Even after the liner was seated, it generally did not possess the flat or smooth characteristics of a new, undistorted liner piece. The tendency for there to occur inadvertent loosening of a liner retained in this manner is still prevalent, and the problem continues to cause difficulty for both container manufacturers, their customers who distribute the products, and ultimately the consumer.